Its a good idea, and it happens already. We've had characters like Steel and the aforementioned Others brought in on the shoulders of more popular and established properties, and both of these examples have gone on to have their own titles and Steel became a member of the League, and for a little while was gaining some traction among the wider DCU (that fell apart, but still). Vibe and Katana got spun out of the JLA title. So it does happen, and sometimes it even works long term, though it seems that characters like this have a hard time establishing themselves away from whatever franchise they came from.
The only thing Im saying is that the race changing is another option. There doesnt seem to be a single solution that works. New characters struggle, supporting cast members brought into their own struggle, legacies who have replaced someone struggle unless that legacy has been dead for decades (such as with Mr. Terrific). I totally support new characters and supporting cast members getting to step up (hell, thats exactly what Wally did originally!). But the race changing thing, while its problematic, is another way to push representation and in my opinion, every effort should be made to that end. And as long as race never mattered to the character, and that character is still written and treated the same way they originally were, I dont see the big deal. In some cases, it doesnt fit. Batman for example, has to be white; his family was old money two hundred years ago when Gotham was built, and back then only white people had that kind of wealth in America. In order to maintain that sense of old money, Bruce has to be a WASP. John Stewart has to be black; he was designed and built off the (unfortunate) blackspoltation era. It's a big part of who he is. But for most characters, it's a non-issue. Its not like being white ever played a major role for Superman, so as long as the primary visuals (cape, shield, spit curl, ect) are there, who gives a damn about skin tone?
In Wally's case, he hasnt been written or treated well. That's the problem, not the color of his skin. And fortunately, the way he's written can always change.